1. Field
One embodiment of the invention relates to a playback apparatus and a playback method for playing back digital content which is stored in a storage medium.
2. Description of the Related Art
In recent years, with the progress of the digital compression-encoding technology of moving pictures, the development of playback apparatuses (players), which can handle HD (High Definition) standard high-resolution video, has been promoted.
In these players, storage media, such as HD DVDs (High Definition Digital Versatile Discs), are used. By using the storage media such as HD DVDs (High Definition Digital Versatile Discs), it is possible to package HD video data and high-quality surround audio data in a single storage medium.
As a technique for protecting digital content, which is stored in a storage medium, from unlawful copy, there is conventionally known an encryption technique such as CSS (Content Scramble System).
Japanese Patent No. 3162046 discloses a stream of digital content such as video data, in which copy control information is embedded. The copy control information is used in order to realize a copy protection function for restricting copy of digital content such as video data.
In the meantime, recently, in order to enhance the interactivity of digital content, the digital content includes not only a video object such as video data, but also various resource files such as sound effects and image data. The resource files are data for interactively playing back the video object. The video object is encrypted. Similarly, the resource files are encrypted.
Prior to playing back digital content, the respective resource files are loaded from the storage medium into a file cache in the player. A necessary resource file is read out from the file cache and is played back. With use of the file cache, there is no necessity to access the storage medium in order to read out the resource file during the process of reading out the video object from the storage medium.
Normally, each resource file is stored in the file cache in the encrypted state. This enables secure handling of resource files even in such a use case that a copy of each resource file is transferred from the file cache to, for example, a storage device provided in the player.
However, in the case where each resource file is stored in the file cache in the encrypted state, decryption of the resource file is required each time the resource file in the file cache is used. If a buffer area, which is different from the file cache, is prepared, it becomes possible to store each decrypted resource file in the buffer area. However, the use of the dedicated buffer area increases the memory size which needs to be implemented in the player, leading to an increase in cost of the player.
It is necessary, therefore, to realize a novel function of securely handling resource files, without the need to provide a dedicated buffer area.